Numerous chemicals have been proposed for the purpose of controlling diseases in agricultural and horticultural crops. For example, Patent Document 1 and Patent Document 2 disclose chemicals containing a 4,4-difluoro-3,4-dihydroisoquinoline derivative represented by general formula (1):

However, a specific method for preparing the aforementioned 4,4-difluoro-3,4-dihydroisoquinoline derivative represented by general formula (1) is not described in the aforementioned patent documents. When producing this group of compounds, an efficient method comprises deoxyfluorinating the ketone group of an isoquinolin-4(3H)-one derivative represented by general formula (4) disclosed in Patent Document 1:

With the foregoing background, there has been a fervent desire for the development of a production method that enables 4,4-difluoro-3,4-dihydroisoquinoline derivatives to be synthesized easily and allows them to be produced on an industrial scale.